Abstract : Metallic debris sensors have been developed for recirculating oil lubrication systems. The in-line monitors apply the principle of X-ray fluorescence. The nucleonic oil debris monitors (ODM's) have been designed and fabricated for use with test cell operations involving aircraft transmissions and gear boxes. ODM's were tested to evaluate their sensitivity, accuracy, and response to lubricant temperature over the range of 100F to 300F. Iron in solution and particles of diameters to 300 micrometers were used for both dynamic and static tests with MIL-L-7808 oil. Both debris mass and rate-of-change outputs are provided. (Modified author abstract)